Chemistry In Industry

Question 1

Describe the method of extracting aluminium from purified aluminium oxide by electrolysis;

Answer 1

After mining and purifying, a white powder (pure aluminium oxide Al2O3) is left.

• Al2O3 has a v high melting point of over 2000 C - melting v expensive
• Instead it is dissolved in molten cryolite (a less common ore of aluminium) to decrease required operating temp to 900 C (cheaper and easier)
• the electrodes are made of graphite - good conductor
• uses a lot of electricity - v expensive
• energy also needed to heat electrolyte mixture to 900 C
• disappearing positive electrodes need frequent replacement
• aluminium comes out as a reasonably cheap and widely used metal

Question 2

Explain how methods of extraction of metals are related to their positions in the reactivity series

Answer 2

Metals that are less reactive than carbon can be extracted by a reduction reaction with carbon:

Heat the ore with carbon monoxide - more reactive elements form compounds more readily. Carbons more reactive than iron/tin/zinc so carbon displaces iron/tin/zinc oxide to form carbon dioxide and iron/tin/zinc

Very reactive metals form v stable ores - difficult to extract. More reactive than carbon - extracted using electrolysis